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Tell me your cracked flexplate stories

Discussion in 'The Garage' started by rafterman191, Dec 3, 2006.

  1. rafterman191

    rafterman191 Registered Member

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    what did it sound like?, how did you diagnose it?, repair process? Someone suggested I may have that problem. I have a nasty loud knock that sounds like a cross between an exhaust leak and a loud knock with a slight mix of metal tingling. Gets louder at higher RPM but when it is just idling, you can almost not even hear it. Also, I have developed a tranny fluid leak somewhere too. Related?
     
  2. 1979jimmy350

    1979jimmy350 1/2 ton status

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    a cracked flex plate will not make noise under load only at low rpms and idle, it sounds like what you are hearing is the exact opposit.
     
  3. rafterman191

    rafterman191 Registered Member

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    Definetely experiencing the opposite. A CK5er had suggested the flex plate. From everything else I had read, as far as the noise and RPM to noise association, it sounds like a crank problem. In other words, scrap the motor.
     
  4. thedrip

    thedrip 1/2 ton status

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    My cracked flexplate made noise all over the place. Idle, High rpm, no load, full throttle up a hill. Sounded like hell. Didn't have a clue what was wrong, I figured I broke some vanes in the torque converter or something like that. Thats the last time I use a flexplate thats hanging on the wall, covered in grease, in a shop used by a dirt track stock car team.
     
  5. 87BrnRsd

    87BrnRsd 1/2 ton status

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    I disagree. When my brothers flexplate cracked, you could only hear it first under load. The first time we heard it was when in 4lo and giving it some good gas to get up a rock. The return trip home you could only hear it if you were beside a concrete divider where the sound bounced back at you, and he had to be giving it at least 1/2 throttle. It took a week or so of getting louder to hear it at idle. Definitely sounded like a rod knock though. Damn thing was cracked almost completley around all of the bolt holes. Only about an inch of metal kept it on there.:eek1:
    -Harrison
     
  6. 3 on the tree

    3 on the tree 1/2 ton status

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    I had one in a Cherokee that was broken around ALL of the TC bolts. It sounded like a rod knock at all rpms, but still started without any weird noises. I pulled the motor cause I thought I had a bad rod bearing:doah: :doah: .
     
  7. rafterman191

    rafterman191 Registered Member

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    This noise definetly came out of right field. There was no warning. Went from running fine to boom, loud.
     
  8. pplblazerdude

    pplblazerdude 1/2 ton status

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    I had one just break on my truck. Mine was a idle based sound and if you gave it gas it went away. You could not hear it once you barely reved it up. It sounded like the truck was going to throw a rod. Ended up my flexplate was in two parts when it was removed. I got real lucky that it didnt blow up and destroy alot of stuff in there.
     
  9. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    Only cracked flex plate I've ever had made no noise what so ever. Didn't know it was cracked till we pullled the motor for an overhaul. Once the motor was out I was able to remove the flexplate and not take any of the bolts out. Totally shocked.
     
  10. big dan

    big dan 1/2 ton status Premium Member

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    when mine cracked it made a light clicking noise at idle and went away at higher rpms. kept getting louder and louder till the center finally busted all the way out. I figured out what it was by looking at it. heard the noise and crawled underneath. looked around using a light and noticed a crack in between the holes. picked up a new but my lazy butt kept driving till it wouldnt start anymore.:D for replacement I took all the bolts out and put 6" long bolts in the two bottom holes, unbolted the tc and slid the tranny back. barely enough room to get my hand in to reach the bolts but it beats having to pull the whole tranny out and stuff it back in.
     
  11. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Mine had the same problem, and was the reason why I took my GMC off the road in the first place, cause I thought I'd blown my engine.

    Mine was like cybrfire's pulled it off by hand without undoing any bolts... Mine made noise at idle, and lower RPMs, but went away with higher rpms. I drove home with the tranny locked in 2nd to keep the noise away, and haven't driven it on the road since, nearly 4 years later :(
     
  12. diesel4me

    diesel4me 1 ton status Premium Member

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    been lucky myself..

    I only had one flexplate that cracked,and I never knew it until I yanked the TH350 out of the truck in favor of an SM465..since I was converting to a manual,I didn't have to replace it..it was cracked about halfway around the bolt circle.. :eek1: --truck only made a few clicking noises,and a few times the starter skipped like it had busted teeth,but otherwise I never suspected the flexplate was cracked!..

    I've seen/heard dozens of other vehicles with broken flexplates,but the funny thing is none seem to sound exactly the same,or get noisy at the same RPM's..loose torque converter bolts do much the same thing too,all sound like a rod is about to make a window in the crankcase..some get quiet if you put it in gear under load,others sound louder when torqued up!..

    My friend drove his 76 Caddy Coupe Deville from Hershey PA to where I used to live in Leominster MA ,about 500 miles,with what he thought to be a rod knock,that got progessively louder with every mile!..when he arrived in his hometown,he drove it right to his mechanic,and called me for a ride home..when I heard the car,I thought sure the motor was junk!..but the mechanic said he'd pull the tranny cover off first--not to assume the motor was rapping..

    --Sure enough,when he pulled on the flex plate,the last remaining 1/8" or so that hadn't cracked,broke off,and it dropped halfway out of the bellhousing!...I bet my friend would have been walking if he drove it even a few more miles,or gave it a bit too much gas on takeoff!--he was glad the motor wasn't rapping...

    Seems not only the big motors with gobs of HP and torque are the only ones that crack flexplates,I've seen many cars do it regardless of motor size or power--everything from 3 cylinder GEO's to monster 500 Caddy motors...:crazy:
     

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